This invention relates to power transmissions and more particularly to power transmissions having multiple countershafts.
Power transmissions with multiple countershafts generally have a housing assembly formed with at least two members that are aligned by dowel pins. These members generally include a casing and an end cover or bell housing. The bell housing generally encloses a torque converter or friction clutch. The countershafts are supported in the casing at one end and in the end cover at the other end. The input shaft is generally supported in the end cover and the output shaft is supported in the casing.
The alignment and parallelism of the shafts is determined by the doweling between the casing and cover and the bearing bores in each of the casing and end cover. The machining of the required dowel and bearing bores is subject to manufacturing tolerances which must be held within close limits for quiet, efficient and durable operation of the transmission. As is well known, close tolerance machining adds to the overall cost of the product.
Also, prior art transmissions use a separate axis for the idler gear in the reverse gear ratio. The preparation of the structure for the idler gear requires additional machining and support material within the casing member of the housing assembly. The overall cost is again affected by the need for this added material, machining and the complexity of the casing casting. The use of a reverse gear idler on a separate axis also affects the numerical value of the reverse ratio making it difficult to provide a reverse ratio equal to the forward low ratio.